1. Field of the Invention
The present invention relates to a non contacting magnetic keyboard having a simple printed circuit construction and with a minimum of network elements.
2. Description of the Prior Art
Keyboards are typically used in a variety of devices including computers, computer terminals, calculators, control panels, telephone devices, etc. The prior art keyboards are generally two types. The older types of keyboards are mechanical and include electrical contacts. More recently keyboards have been designed which may be referred to as solid state non contacting types. It will be appreciated that the mechanical types of keyboards suffer from mechanical wear, erosion and corrosion of contacts, etc. which limit their useful life and reliability. The solid state types of keyboards include; electro magnetic, capacitive, photo electric, hall effect types, etc. Although the solid state types represent an improvement over the mechanical types, most of the solid state types suffer from high cost while still exhibiting problems with performance and reliability. Therefore, there have been numerous attempts to provide improved non-contacting keyboards to eliminate the above problems.
As an example, Cochran et al. U.S. Pat. No. 3,668,697, Holz U.S. Pat. No. 3,683,361 and Bernin U.S. Pat. No. 4,300,127 all include the use of a printed circuit board with printed circuit elements forming excitation and sensing elements in a network and with a movable element controlling the passage of a signal from the excitation to the sensing elements. Additionally, the Bernin et al. U.S. Pat. No. 3,918,051 discloses a non-contacting keyboard using a balanced drive wire system. The Cochran et al. and Bernin U.S. Pat. No. 4,300,127 both use a balanced system and incorporate a separate balance or bucking coil arrangement for each actuating position. The Bernin et al. U.S. Pat. No. 3,918,051 has a complicated system in using two additional common wires additionally to the excitation and sensing wires. The Holz patent does not include any balancing to improve the keyboard performance. However, as will be seen, these prior art devices do not incorporate the advantages of the present invention.